The Syrian army on Sunday intensified its bombing against Sunni neighborhoods of the city of Homs, in part controlled by the rebels, killing at least eleven people and wounding dozens more, according to opposition activists. "About 85% of Homs is now suffering from mortar shelling or firing of heavy machine guns," said Abu Imad, a local opposition activists.

"Dozens of wounded were not treated after all local hospitals have been under the control of the Shabbiha (pro-regime militias). The dead are the lucky ones," he said. This came one day after the UN observers suspended their operations following the upsurge in violence.

Meanwhile, the Syrian opposition on Sunday urged the UN to send armed peacekeepers to Syria and to pass a resolution forcing the regime to stop the repression. This request comes on the eve of the opening of the G20 summit in Mexico, where Syria is expected to be on the agenda of U.S. President Barack Obama during his meetings with Russia's Vladimir Putin and Chinese President Hu Jintao.

In a statement, the main opposition body, the Syrian National Council (SNC), has asked the UN to "rapidly adopt a resolution under Chapter VII (in its charter) to arm the observers (...) in order they carry out their work safely, force the regime to stop the killing and to implement the plan by international envoy Kofi Annan "to end the crisis."

The SNC said it was "surprised" by the decision of UN mission chief in Syria Robert Mood to suspended operations of its 300 observers.

According to a report by Syrian Observatory for Human Rights (SOHR) dated Thursday, violence killed at least 3,353 people since April 12, the date of formal entry into force of the un cease-fire.